Does anyone have experience with a lightweight crankpully on his FE3? I have one lying around and would soon be able to use it if I'm replacing my camshaft gears. I read on different forums different opinions because they are solid aluminum and are not damping.

The engine is a almost stock high comp FE-DOHC with a 70 mm throttlebody and athermarket exhaustheaders

The alternator and other accessories do provide quite a bit of dampening though, it's when you run an engine without load other than camshaft(s) or a long crank (I6) you will have real problems. Old 8-valve FE's had solid pulleys and I don't remember them having problems with crank fatigue. Still you might want to have the increased dampening on high output engine tunes.

A lightweight pulley with tungsten rods embedded in urethane on the rim would be an interesting idea, it should have pretty high hysteresis for good dampening while having less rotational inertia and weight than the original. Pulley does have pretty insignificant impact on engine response so it's probably more an emotional issue than anything else.

The FET that is in my GC has a solid pulley and that was OEM fitment, and I still have it on there. Never had any issues to date. AUSDM cars all had balancers on the cranks, my engine is ex JDM, and other JDM imports all had solid pulleys too.
They were not interchangeable as the solid pulleys were 6 bolt and the harmonic balancer type were 4 bolt.

I am not sure that harmonic balancers on I4s are there to protect the crank but maybe to assist in reducing accessory belt noise to help lower the NVH.

NVH indeed seems to be the main motivation behind the change to dampened unit in the later FE's.

Still, I don't find much improvement in going from stock iron pulley to similar solid alloy pulley, but of course if you need alternative drive ratios for accessories, or want to use different belts, not needing a dampened pulley makes things far simpler.